Precalculus Examples

$x - 2 y = - 5$ , $(0, 4)$

Step 1

Solve $x - 2 y = - 5$ .

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Step 1.1

Subtract $x$ from both sides of the equation.

$- 2 y = - 5 - x$

Step 1.2

Divide each term in $- 2 y = - 5 - x$ by $- 2$ and simplify.

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Step 1.2.1

Divide each term in $- 2 y = - 5 - x$ by $- 2$ .

$\frac{- 2 y}{- 2} = \frac{- 5}{- 2} + \frac{- x}{- 2}$

Step 1.2.2

Simplify the left side.

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Step 1.2.2.1

Cancel the common factor of $- 2$ .

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Step 1.2.2.1.1

Cancel the common factor.

$\frac{- 2 y}{- 2} = \frac{- 5}{- 2} + \frac{- x}{- 2}$

Step 1.2.2.1.2

Divide $y$ by $1$ .

$y = \frac{- 5}{- 2} + \frac{- x}{- 2}$

Step 1.2.3

Simplify the right side.

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Step 1.2.3.1

Simplify each term.

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Step 1.2.3.1.1

Dividing two negative values results in a positive value.

$y = \frac{5}{2} + \frac{- x}{- 2}$

Step 1.2.3.1.2

Dividing two negative values results in a positive value.

$y = \frac{5}{2} + \frac{x}{2}$

Step 2

Find the slope when $y = \frac{5}{2} + \frac{x}{2}$ .

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Step 2.1

Rewrite in slope-intercept form.

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Step 2.1.1

The slope-intercept form is $y = m x + b$ , where $m$ is the slope and $b$ is the y-intercept.

$y = m x + b$

Step 2.1.2

Reorder $\frac{5}{2}$ and $\frac{x}{2}$ .

$y = \frac{x}{2} + \frac{5}{2}$

Step 2.1.3

Reorder terms.

$y = \frac{1}{2} x + \frac{5}{2}$

Step 2.2

Using the slope-intercept form, the slope is $\frac{1}{2}$ .

$m = \frac{1}{2}$

Step 3

The equation of a perpendicular line must have a slope that is the negative reciprocal of the original slope.

$m_{perpendicular} = - \frac{1}{\frac{1}{2}}$

Step 4

Simplify $- \frac{1}{\frac{1}{2}}$ to find the slope of the perpendicular line.

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Step 4.1

Multiply the numerator by the reciprocal of the denominator.

$m_{perpendicular} = - (1 \cdot 2)$

Step 4.2

Multiply $- (1 \cdot 2)$ .

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Step 4.2.1

Multiply $2$ by $1$ .

$m_{perpendicular} = - 1 \cdot 2$

Step 4.2.2

Multiply $- 1$ by $2$ .

$m_{perpendicular} = - 2$

Step 5

Find the equation of the perpendicular line using the point-slope formula.

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Step 5.1

Use the slope $- 2$ and a given point $(0, 4)$ to substitute for $x_{1}$ and $y_{1}$ in the point-slope form $y - y_{1} = m (x - x_{1})$ , which is derived from the slope equation $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (4) = - 2 \cdot (x - (0))$

Step 5.2

Simplify the equation and keep it in point-slope form.

$y - 4 = - 2 \cdot (x + 0)$

Step 6

Solve for $y$ .

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Step 6.1

Add $x$ and $0$ .

$y - 4 = - 2 x$

Step 6.2

Add $4$ to both sides of the equation.

$y = - 2 x + 4$

Step 7